﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System;
using System.IO;
using SkiaSharp;
using System.Drawing;

// copy from : https://github.com/avianbc/NGif

namespace Lazy.Captcha.Core.Generator.Image.Gif
{


    #region .NET Disclaimer/Info
    //===============================================================================
    //
    // gOODiDEA, uland.com
    //===============================================================================
    //
    // $Header :		$  
    // $Author :		$
    // $Date   :		$
    // $Revision:		$
    // $History:		$  
    //  
    //===============================================================================
    #endregion

    #region Java
    /**
     * Class AnimatedGifEncoder - Encodes a GIF file consisting of one or
     * more frames.
     * <pre>
     * Example:
     *    AnimatedGifEncoder e = new AnimatedGifEncoder();
     *    e.start(outputFileName);
     *    e.setDelay(1000);   // 1 frame per sec
     *    e.addFrame(image1);
     *    e.addFrame(image2);
     *    e.finish();
     * </pre>
     * No copyright asserted on the source code of this class.  May be used
     * for any purpose, however, refer to the Unisys LZW patent for restrictions
     * on use of the associated LZWEncoder class.  Please forward any corrections
     * to kweiner@fmsware.com.
     *
     * @author Kevin Weiner, FM Software
     * @version 1.03 November 2003
     *
     */
    #endregion

    #region Modified By Phil Garcia
    /* 
     * Modified by Phil Garcia (phil@thinkedge.com) 
        1. Add support to output the Gif to a MemoryStream (9/2/2005)

    */
    #endregion
    public class AnimatedGifEncoder
    {
        protected int width; // image size
        protected int height;
        protected SKColor transparent = SKColor.Empty; // transparent color if given
        protected int transIndex; // transparent index in color table
        protected int repeat = -1; // no repeat
        protected int delay = 0; // frame delay (hundredths)
        protected bool started = false; // ready to output frames
                                        //	protected BinaryWriter bw;
        protected MemoryStream ms;
        //		protected FileStream fs;

        protected SKImage image; // current frame
        protected byte[] pixels; // BGR byte array from frame
        protected byte[] indexedPixels; // converted frame indexed to palette
        protected int colorDepth; // number of bit planes
        protected byte[] colorTab; // RGB palette
        protected bool[] usedEntry = new bool[256]; // active palette entries
        protected int palSize = 7; // color table size (bits-1)
        protected int dispose = -1; // disposal code (-1 = use default)
        protected bool closeStream = false; // close stream when finished
        protected bool firstFrame = true;
        protected bool sizeSet = false; // if false, get size from first frame
        protected int sample = 10; // default sample interval for quantizer

        /**
         * Sets the delay time between each frame, or changes it
         * for subsequent frames (applies to last frame added).
         *
         * @param ms int delay time in milliseconds
         */
        public void SetDelay(int ms)
        {
            delay = (int)Math.Round(ms / 10.0f);
        }

        /**
         * Sets the GIF frame disposal code for the last added frame
         * and any subsequent frames.  Default is 0 if no transparent
         * color has been set, otherwise 2.
         * @param code int disposal code.
         */
        public void SetDispose(int code)
        {
            if (code >= 0)
            {
                dispose = code;
            }
        }

        /**
         * Sets the number of times the set of GIF frames
         * should be played.  Default is 1; 0 means play
         * indefinitely.  Must be invoked before the first
         * image is added.
         *
         * @param iter int number of iterations.
         * @return
         */
        public void SetRepeat(int iter)
        {
            if (iter >= 0)
            {
                repeat = iter;
            }
        }

        /**
         * Sets the transparent color for the last added frame
         * and any subsequent frames.
         * Since all colors are subject to modification
         * in the quantization process, the color in the final
         * palette for each frame closest to the given color
         * becomes the transparent color for that frame.
         * May be set to null to indicate no transparent color.
         *
         * @param c Color to be treated as transparent on display.
         */
        public void SetTransparent(SKColor c)
        {
            transparent = c;
        }

        /**
         * Adds next GIF frame.  The frame is not written immediately, but is
         * actually deferred until the next frame is received so that timing
         * data can be inserted.  Invoking <code>finish()</code> flushes all
         * frames.  If <code>setSize</code> was not invoked, the size of the
         * first image is used for all subsequent frames.
         *
         * @param im BufferedImage containing frame to write.
         * @return true if successful.
         */
        public bool AddFrame(SKImage im)
        {
            if ((im == null) || !started)
            {
                return false;
            }
            bool ok = true;
            try
            {
                if (!sizeSet)
                {
                    // use first frame's size
                    SetSize(im.Width, im.Height);
                }
                image = im;
                GetImagePixels(); // convert to correct format if necessary
                AnalyzePixels(); // build color table & map pixels
                if (firstFrame)
                {
                    WriteLSD(); // logical screen descriptior
                    WritePalette(); // global color table
                    if (repeat >= 0)
                    {
                        // use NS app extension to indicate reps
                        WriteNetscapeExt();
                    }
                }
                WriteGraphicCtrlExt(); // write graphic control extension
                WriteImageDesc(); // image descriptor
                if (!firstFrame)
                {
                    WritePalette(); // local color table
                }
                WritePixels(); // encode and write pixel data
                firstFrame = false;
            }
            catch (IOException)
            {
                ok = false;
            }

            return ok;
        }

        /**
         * Flushes any pending data and closes output file.
         * If writing to an OutputStream, the stream is not
         * closed.
         */
        public bool Finish()
        {
            if (!started) return false;
            bool ok = true;
            started = false;
            try
            {
                ms.WriteByte(0x3b); // gif trailer
                ms.Flush();
                if (closeStream)
                {
                    //					ms.Close();
                }
            }
            catch (IOException)
            {
                ok = false;
            }

            // reset for subsequent use
            transIndex = 0;
            //			fs = null;
            image = null;
            pixels = null;
            indexedPixels = null;
            colorTab = null;
            closeStream = false;
            firstFrame = true;

            return ok;
        }

        /**
         * Sets frame rate in frames per second.  Equivalent to
         * <code>setDelay(1000/fps)</code>.
         *
         * @param fps float frame rate (frames per second)
         */
        public void SetFrameRate(float fps)
        {
            if (fps != 0f)
            {
                delay = (int)Math.Round(100f / fps);
            }
        }

        /**
         * Sets quality of color quantization (conversion of images
         * to the maximum 256 colors allowed by the GIF specification).
         * Lower values (minimum = 1) produce better colors, but slow
         * processing significantly.  10 is the default, and produces
         * good color mapping at reasonable speeds.  Values greater
         * than 20 do not yield significant improvements in speed.
         *
         * @param quality int greater than 0.
         * @return
         */
        public void SetQuality(int quality)
        {
            if (quality < 1) quality = 1;
            sample = quality;
        }

        /**
         * Sets the GIF frame size.  The default size is the
         * size of the first frame added if this method is
         * not invoked.
         *
         * @param w int frame width.
         * @param h int frame width.
         */
        public void SetSize(int w, int h)
        {
            if (started && !firstFrame) return;
            width = w;
            height = h;
            if (width < 1) width = 320;
            if (height < 1) height = 240;
            sizeSet = true;
        }

        /**
         * Initiates GIF file creation on the given stream.  The stream
         * is not closed automatically.
         *
         * @param os OutputStream on which GIF images are written.
         * @return false if initial write failed.
         */

        public bool Start(MemoryStream os)
        {
            if (os == null) return false;
            bool ok = true;
            closeStream = false;
            ms = os;
            try
            {
                WriteString("GIF89a"); // header
            }
            catch (IOException)
            {
                ok = false;
            }
            return started = ok;
        }

        /**
         * Initiates writing of a GIF file to a memory stream.
         *
         * @return false if open or initial write failed.
         */
        public bool Start()
        {
            bool ok = true;
            try
            {
                ok = Start(new MemoryStream(10 * 1024));
                closeStream = true;
            }
            catch (IOException)
            {
                ok = false;
            }
            return started = ok;
        }

        /**
         * Initiates writing of a GIF file with the specified name.
         *
         * @return false if open or initial write failed.
         */
        public bool Output(string file)
        {
            try
            {
                FileStream fs = new FileStream(file, FileMode.OpenOrCreate, FileAccess.Write, FileShare.None);
                fs.Write(ms.ToArray(), 0, (int)ms.Length);
                fs.Close();
            }
            catch (IOException)
            {
                return false;
            }
            return true;
        }

        public MemoryStream Output()
        {
            return ms;
        }

        /**
         * Analyzes image colors and creates color map.
         */
        protected void AnalyzePixels()
        {
            int len = pixels.Length;
            int nPix = len / 3;
            indexedPixels = new byte[nPix];
            NeuQuant nq = new NeuQuant(pixels, len, sample);
            // initialize quantizer
            colorTab = nq.Process(); // create reduced palette
                                     // convert map from BGR to RGB
                                     //			for (int i = 0; i < colorTab.Length; i += 3) 
                                     //			{
                                     //				byte temp = colorTab[i];
                                     //				colorTab[i] = colorTab[i + 2];
                                     //				colorTab[i + 2] = temp;
                                     //				usedEntry[i / 3] = false;
                                     //			}
                                     // map image pixels to new palette
            int k = 0;
            for (int i = 0; i < nPix; i++)
            {
                int index =
                    nq.Map(pixels[k++] & 0xff,
                    pixels[k++] & 0xff,
                    pixels[k++] & 0xff);
                usedEntry[index] = true;
                indexedPixels[i] = (byte)index;
            }
            pixels = null;
            colorDepth = 8;
            palSize = 7;
            // get closest match to transparent color if specified
            if (transparent != SKColor.Empty)
            {
                //transIndex = FindClosest(transparent);
                transIndex = nq.Map(transparent.Blue, transparent.Green, transparent.Red);
            }
        }

        /**
         * Returns index of palette color closest to c
         *
         */
        protected int FindClosest(SKColor c)
        {
            if (colorTab == null) return -1;
            int r = c.Red;
            int g = c.Green;
            int b = c.Blue;
            int minpos = 0;
            int dmin = 256 * 256 * 256;
            int len = colorTab.Length;
            for (int i = 0; i < len;)
            {
                int dr = r - (colorTab[i++] & 0xff);
                int dg = g - (colorTab[i++] & 0xff);
                int db = b - (colorTab[i] & 0xff);
                int d = dr * dr + dg * dg + db * db;
                int index = i / 3;
                if (usedEntry[index] && (d < dmin))
                {
                    dmin = d;
                    minpos = index;
                }
                i++;
            }
            return minpos;
        }

        /**
         * Extracts image pixels into byte array "pixels"
         */
        protected void GetImagePixels()
        {
            int w = image.Width;
            int h = image.Height;
            //		int type = image.GetType().;
            if ((w != width) || (h != height))
            {
                // create new image with right size/format
                using (var temp = new SKBitmap(width, height))
                {
                    using (var canvas = new SKCanvas(temp))
                    {
                        canvas.DrawBitmap(SKBitmap.FromImage(image), 0, 0);
                        image = SKImage.FromBitmap(temp);
                    }
                }
            }
            /*
                ToDo:
                improve performance: use unsafe code 
            */
            pixels = new Byte[3 * image.Width * image.Height];
            int count = 0;
            SKBitmap tempBitmap = SKBitmap.FromImage(image);
            for (int th = 0; th < image.Height; th++)
            {
                for (int tw = 0; tw < image.Width; tw++)
                {
                    SKColor color = tempBitmap.GetPixel(tw, th);
                    pixels[count] = color.Red;
                    count++;
                    pixels[count] = color.Green;
                    count++;
                    pixels[count] = color.Blue;
                    count++;
                }
            }

            //		pixels = ((DataBufferByte) image.getRaster().getDataBuffer()).getData();
        }

        /**
         * Writes Graphic Control Extension
         */
        protected void WriteGraphicCtrlExt()
        {
            ms.WriteByte(0x21); // extension introducer
            ms.WriteByte(0xf9); // GCE label
            ms.WriteByte(4); // data block size
            int transp, disp;
            if (transparent == SKColor.Empty)
            {
                transp = 0;
                disp = 0; // dispose = no action
            }
            else
            {
                transp = 1;
                disp = 2; // force clear if using transparent color
            }
            if (dispose >= 0)
            {
                disp = dispose & 7; // user override
            }
            disp <<= 2;

            // packed fields
            ms.WriteByte(Convert.ToByte(0 | // 1:3 reserved
                disp | // 4:6 disposal
                0 | // 7   user input - 0 = none
                transp)); // 8   transparency flag

            WriteShort(delay); // delay x 1/100 sec
            ms.WriteByte(Convert.ToByte(transIndex)); // transparent color index
            ms.WriteByte(0); // block terminator
        }

        /**
         * Writes Image Descriptor
         */
        protected void WriteImageDesc()
        {
            ms.WriteByte(0x2c); // image separator
            WriteShort(0); // image position x,y = 0,0
            WriteShort(0);
            WriteShort(width); // image size
            WriteShort(height);
            // packed fields
            if (firstFrame)
            {
                // no LCT  - GCT is used for first (or only) frame
                ms.WriteByte(0);
            }
            else
            {
                // specify normal LCT
                ms.WriteByte(Convert.ToByte(0x80 | // 1 local color table  1=yes
                    0 | // 2 interlace - 0=no
                    0 | // 3 sorted - 0=no
                    0 | // 4-5 reserved
                    palSize)); // 6-8 size of color table
            }
        }

        /**
         * Writes Logical Screen Descriptor
         */
        protected void WriteLSD()
        {
            // logical screen size
            WriteShort(width);
            WriteShort(height);
            // packed fields
            ms.WriteByte(Convert.ToByte(0x80 | // 1   : global color table flag = 1 (gct used)
                0x70 | // 2-4 : color resolution = 7
                0x00 | // 5   : gct sort flag = 0
                palSize)); // 6-8 : gct size

            ms.WriteByte(0); // background color index
            ms.WriteByte(0); // pixel aspect ratio - assume 1:1
        }

        /**
         * Writes Netscape application extension to define
         * repeat count.
         */
        protected void WriteNetscapeExt()
        {
            ms.WriteByte(0x21); // extension introducer
            ms.WriteByte(0xff); // app extension label
            ms.WriteByte(11); // block size
            WriteString("NETSCAPE" + "2.0"); // app id + auth code
            ms.WriteByte(3); // sub-block size
            ms.WriteByte(1); // loop sub-block id
            WriteShort(repeat); // loop count (extra iterations, 0=repeat forever)
            ms.WriteByte(0); // block terminator
        }

        /**
         * Writes color table
         */
        protected void WritePalette()
        {
            ms.Write(colorTab, 0, colorTab.Length);
            int n = (3 * 256) - colorTab.Length;
            for (int i = 0; i < n; i++)
            {
                ms.WriteByte(0);
            }
        }

        /**
         * Encodes and writes pixel data
         */
        protected void WritePixels()
        {
            LZWEncoder encoder =
                new LZWEncoder(width, height, indexedPixels, colorDepth);
            encoder.Encode(ms);
        }

        /**
         *    Write 16-bit value to output stream, LSB first
         */
        protected void WriteShort(int value)
        {
            ms.WriteByte(Convert.ToByte(value & 0xff));
            ms.WriteByte(Convert.ToByte((value >> 8) & 0xff));
        }

        /**
         * Writes string to output stream
         */
        protected void WriteString(String s)
        {
            char[] chars = s.ToCharArray();
            for (int i = 0; i < chars.Length; i++)
            {
                ms.WriteByte((byte)chars[i]);
            }
        }
    }

}
